Semiconductor laser module

ABSTRACT

A semiconductor laser module includes a package; a plurality of semiconductor laser elements provided in the package; a member having a plurality of mounting surfaces on which the semiconductor laser elements are mounted, the mounting surfaces being separated from a bottom surface of the package by respective distances, the distances being gradually different from each other in a manner that the mounting surfaces as a whole form a step-like form; a plurality of lenses collimating respective laser beams emitted from the semiconductor laser elements; a plurality of reflection mirrors reflecting the respective laser beams; a condenser lens unit condensing the laser beams; an optical fiber where the optical beams condensed by the condenser lenses are optically coupled; and an optical filter disposed on optical lines of the respective laser beams reflected by the reflection mirrors and reflecting light having wavelengths different from the wavelengths of the laser beams.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of applicationSer. No. 15/062,744 filed on Mar. 7, 2016 which is a continuation of PCTInternational Application No. PCT/JP2014/074306 filed on Sep. 12, 2014which claims the benefit of priority from U.S. Provisional PatentApplication No. 61/877,069 filed on Sep. 12, 2013 and Japanese PatentApplication No. 2014-026241 filed on Feb. 14, 2014, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a semiconductor laser module.

2. Description of the Related Art

Conventionally, a method has been known, in a case where, in asemiconductor laser module, a laser light is output from an opticalfiber, a laser light emitted from a semiconductor laser element fixed ata predetermined position on a package is condensed by a lens or the liketo make the condensed laser light coupled to an optical fiber (forexample, see Japanese Patent Application Laid-open Publication No.2004-96088).

In such a light coupling method, if the semiconductor laser element ishigh in output, an adhesive fixing the optical fiber and a coatedportion of the optical fiber are damaged by heat produced by opticalabsorption and reliability may decrease sometimes. For that reason,conventionally, a method of inserting an optical fiber through atransparent glass capillary to fix the optical fiber is known (forexample, see Japanese Patent Application Laid-open Publication No.2004-354771).

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

In accordance with one aspect of the present invention, a semiconductorlaser module includes a package; a plurality of semiconductor laserelements provided in the package; a member having a plurality ofmounting surfaces on which the semiconductor laser elements are mounted,the mounting surfaces being separated from a bottom surface of thepackage by respective distances, the distances being gradually differentfrom each other in a manner that the mounting surfaces as a whole form astep-like form; a plurality of lenses collimating respective laser beamsemitted from the semiconductor laser elements; a plurality of reflectionmirrors reflecting the respective laser beams; a condenser lens unitcondensing the laser beams; an optical fiber where the optical beamscondensed by the condenser lenses are optically coupled; and an opticalfilter disposed on optical lines of the respective laser beams reflectedby the reflection mirrors and reflecting light having wavelengthsdifferent from the wavelengths of the laser beams.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a semiconductor laser moduleaccording to an embodiment of the present invention;

FIG. 2 is a schematic partially cutout view showing a side surface ofthe semiconductor laser module shown in FIG. 1;

FIG. 3 is an enlarged schematic cross-sectional view of an opticalfiber, a glass capillary, and a light-absorbing element of thesemiconductor laser module shown in FIG. 1;

FIG. 4 is an enlarged schematic partially cutout view of a firstlight-blocking portion of the semiconductor laser module shown in FIG.1;

FIG. 5A is an enlarged view of a part where an optical filer is includedof the semiconductor laser module of FIG. 1;

FIG. 5B is a view illustrating a part where light reflected by theoptical filter irradiates on the first light-blocking portion of FIG. 4;

FIG. 6 is a schematic view showing a relationship between angle of alight leaking from the optical fiber relative to the center of theoptical fiber and an optical power;

FIG. 7 is an enlarged schematic partially cutout view of a firstlight-blocking portion of a semiconductor laser module according to amodified example;

FIG. 8 is a schematic view showing refractive index of a cross sectionof the glass capillary orthogonal to the longitudinal direction of theoptical fiber of the semiconductor laser module according to themodified example;

FIG. 9 is a schematic cross-sectional view of the cross section of theglass capillary orthogonal to the longitudinal direction of the opticalfiber of the semiconductor laser module according to the modifiedexample;

FIG. 10 is a schematic cross-sectional view of the cross section of theglass capillary orthogonal to the longitudinal direction of the opticalfiber of the semiconductor laser module according to the modifiedexample;

FIG. 11 is a schematic cross-sectional view of the cross section of theglass capillary orthogonal to the longitudinal direction of the opticalfiber of the semiconductor laser module according to the modifiedexample;

FIG. 12 is a schematic cross-sectional view of the cross section of theglass capillary orthogonal to the longitudinal direction of the opticalfiber of the semiconductor laser module according to the modifiedexample;

FIG. 13 is a schematic view showing a relationship between distance froman end surface, at an incident side, of the glass capillary in thelongitudinal direction of the optical fiber and optical absorptivity ofthe light-absorbing element of the semiconductor laser module accordingto the modified example; and

FIG. 14 is an enlarged schematic cross-sectional view of an opticalfiber, a glass capillary, and a light-absorbing element of thesemiconductor laser module according to the modified example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of a semiconductor laser module according to thepresent invention will be explained in detail with reference to thedrawings. The present invention is not limited to these embodiments. Inall the drawings, identical or corresponding elements are given samereference numerals appropriately. Moreover, it should be noted that thedrawings show schematic examples. Accordingly, a relationship betweenrespective elements may be different from real values. Among thedrawings, there may be parts where the relationships and ratios of theshown sizes are different from one another.

Inventors of the subject application found a problem that an adhesiveand a coated portion may be damaged by produced heat even if a glasscapillary is used in the semiconductor laser module.

In contrast, according to the embodiment described below, a highlyreliable semiconductor laser module is achieved.

To start with, a configuration of a semiconductor laser module accordingto an embodiment of the present invention will be explained. FIG. 1 is aschematic plan view of the semiconductor laser module according to theembodiment of the present invention. FIG. 2 is a schematic partiallycutout view showing a side surface of the semiconductor laser moduleshown in FIG. 1. A semiconductor laser module 100 according to thepresent embodiment includes a package 101 as a housing,LD-height-adjusting plate 102, sub-mounts 103-1 to 6, and sixsemiconductor laser elements 104-1 to 6 mounted in order inside thepackage 101. Although the package 101 is provided with a lid 101 a asshown in FIG. 2, the lid of the package 101 is omitted to be shown inFIG. The semiconductor laser module 100 includes a lead pin 105injecting a current to the semiconductor laser elements 104-1 to 6. Thesemiconductor laser module 100 includes first lenses 106-1 to 6, secondlenses 107-1 to 6, mirrors 108-1 to 6, a third lens 109, an opticalfilter 110, and a fourth lens 111, as optical elements disposed in orderon optical paths of laser lights outputted from the semiconductor laserelements 104-1 to 6. The first lenses 106-1 to 6, the second lenses107-1 to 6, the mirrors 108-1 to 6, the third lens 109, the opticalfilter 110, and the fourth lens 111 are fixed inside the package 101respectively. The semiconductor laser module 100 further includes anoptical fiber 112 disposed to face the fourth lens 111. An end, at aside into which the laser light is incident, of the optical fiber 112 isenclosed inside the package 101.

As shown in FIG. 2, the semiconductor laser elements 104-1 to 6 aredisposed on steps of the LD-height-adjusting plate 102 and inside thepackage 101. Each one of the first lenses 106-1 to 6, each one of thesecond lenses 107-1 to 6, and each one of the mirrors 108-1 to 6 aredisposed at a corresponding height of each of the semiconductor laserelements.

A loose tube 115 is provided to an insertion portion, of the opticalfiber 112, to be inserted into the package 101. A boot 114 is fittedoutwardly on a portion of the package 101 to cover a portion of theloose tube 115 and the insertion portion.

As shown in FIG. 2, the optical fiber 112 is inserted into a glasscapillary 116 as an optical component. The optical fiber 112 is providedwith a coated portion 112 a. However, the coated portion 112 a isremoved at a portion, being inserted into the glass capillary 116, ofthe optical fiber 112. The optical fiber 112 is provided with aprotrusion portion 112 b, at a portion at an incident side, projectingfrom the glass capillary 116. An outer periphery of the glass capillary116 is covered with a light-absorbing element 117. The light-absorbingelement 117 is fixed to the package 101. A second light-blocking portion118 is disposed at a laser-light-emitting end side of the glasscapillary 116. The second light-blocking portion 118 fits thelight-absorbing element 117 at a laser-light-emitting end side of thelight-absorbing element 117. The loose tube 115 is inserted through aportion of the second light-blocking portion 118.

Hereafter, a configuration in the vicinity of the optical fiber 112 ofthe semiconductor laser module 100 will be explained in detail. FIG. 3is an enlarged schematic cross-sectional view of the optical fiber, theglass capillary, and the light-absorbing element, of the semiconductorlaser module shown in FIG. 1. As shown in FIG. 3, the optical fiber 112includes a core portion 112 c and a cladding portion 112 d.

The optical fiber 112 is inserted through the glass capillary 116. Theoptical fiber 112 and the glass capillary 116 are fastened with afirst-fixing agent 119. The glass capillary 116 is inserted through thelight-absorbing element 117. The glass capillary 116 and thelight-absorbing element 117 are fastened with a second-fixing agent 120.

A first light-blocking portion 113 is disposed between an end, intowhich the laser light is incident, of the optical fiber 112 and theglass capillary 116.

Hereafter, each of elements constituting the semiconductor laser module100 shown in FIGS. 1 to 3 will be explained in further detail. It ispreferable that the package 101 as a housing be made of a material ofsuperior thermal conductivity for restraining an increase in temperaturethereinside, and the package 101 may be made of a metal component madeof various kinds of metal. It is preferable that, as shown in FIG. 2, abottom surface of the package 101 be separated from a plane, on whichthe semiconductor laser module 100 is disposed, in an area in which theglass capillary 116 is disposed. Hereby, it is possible to decrease aninfluence of warp of the bottom surface of the package 101 when fixingthe package 101 with a screw or the like.

As described above, the LD-height-adjusting plate 102 fixed in thepackage 101 is configured to adjust heights of the semiconductor laserelements 104-1 to 6 so that optical paths of the laser lights outputtedby the semiconductor laser elements 104-1 to 6 do not interfere witheach other. The LD-height-adjusting plate 102 may be configured to beunited with the package 101.

The sub-mounts 103-1 to 6 are fixed on the LD-height-adjusting plate 102to assist radiation of the semiconductor laser elements 104-1 to 6mounted thereon. For that purpose, it is preferable that the sub-mounts103-1 to 6 be made of a material of superior thermal conductivity, andthe sub-mounts 103-1 to 6 may be metal components made of various kindsof metal.

The semiconductor laser elements 104-1 to 6 are high outputsemiconductor laser elements, of which optical power of the laser lightbeing outputted is equal to or greater than 1 W, or equal to or greaterthan 10 W. In the present embodiment, the optical power of the laserlight outputted from the semiconductor laser elements 104-1 to 6 is, forexample, 11 W. The semiconductor laser elements 104-1 to 6 output, forexample, laser lights at wavelengths of 900 nm to 1000 nm. The number ofthe semiconductor laser elements 104-1 to 6 may be more than one likethe semiconductor laser module 100 according to the present embodiment.Alternatively, the number may be one and will not be limitedspecifically.

The lead pins 105 supplies electric power to the semiconductor laserelements 104-1 to 6 via a bonding wire not shown in the drawings. Theelectric power being supplied may be at a constant voltage or at amodulated voltage.

The first lenses 106-1 to 6 are cylindrical lenses, of which focaldistances are, for example, 0.3 mm. Each one of the first lenses 106-1to 6 is disposed at a position at which a light being outputted fromeach corresponding one of the semiconductor laser elements becomes anapproximate collimated light in the vertical direction.

The second lenses 107-1 to 6 are cylindrical lenses of which focaldistances are, for example, 5 mm. Each one of the second lenses 107-1 to6 is disposed at a position at which a light being outputted from eachcorresponding one of the semiconductor laser elements becomes anapproximate collimated light in the horizontal direction.

The mirrors 108-1 to 6 may be mirrors provided with various kinds ofmetal layers or dielectric layers, and it is preferable thatreflectivities thereof be as high as possible at wavelengths of thelaser lights being outputted from the semiconductor laser elements 104-1to 6. The mirrors 108-1 to 6 are capable of fine-tuning a direction ofthe reflected laser light, of a corresponding one of the semiconductorlaser elements, to be coupled to the optical fiber 112 desirably.

The third lens 109 and the fourth lens 111 are cylindrical lenses ofwhich focal distances are, for example, 12 mm and 5 mm respectively andof which curvatures are orthogonal to each other. The third lens 109 andthe fourth lens 111 condense the laser lights outputted by thesemiconductor laser elements 104-1 to 6 to couple the condensed laserlights to the optical fiber 112 desirably. Positions of the third lens109 and the fourth lens 111 relative to the optical fiber 112 areadjusted so that coupling efficiencies for the laser lights outputted bythe semiconductor laser elements 104-1 to 6 to the optical fiber 112are, for example, equal to or greater than 85%.

The optical filter 110 is a low-pass filter reflecting lights, forexample, at wavelengths of 1060 nm to 1080 nm and transmitting lights atwavelengths of 900 nm to 1000 nm therethrough. As a result, the opticalfilter 110 makes laser lights outputted by the semiconductor laserelements 104-1 to 6 be transmitted therethrough and prevents the lightat wavelengths of 1060 nm to 1080 nm from being irradiated to thesemiconductor laser elements 104-1 to 6 from outside. The optical filter110 is disposed to be angled relative to the optical axis of the laserlight so that the laser lights outputted by the semiconductor laserelements 104-1 to 6 and slightly reflected by the optical filter 110 donot return to the semiconductor laser elements 104-1 to 6.

The optical filter 110 is located between two condenser lenses, that it,the third lens 109 and the fourth lens 111. It is preferable that theoptical filter 110 be tilted by, for example, two degrees or more. Theoptical filter 110 reflects light having a wavelength in a range, forexample, of 1060 nm to 1080 nm, the light being propagated through theoptical fiber 112 and being irradiated from outside of the opticalfilter 110. In this case, due to the tilt of the optical filter 110, itbecomes possible to prevent the light, which is reflected from theoptical filter 110, from being re-coupled in the optical fiber 112 orburning out the adhesive fixing for the optical fiber 112. Further, dueto the location of the optical filter 110 between the two condenserlenses, it becomes possible to prevent the light from being recollectednear the optical fiber 112, the light being propagated through theoptical fiber 112 from outside, irradiated to the optical filter 110,and then reflected by the optical filter 110. By doing this, it becomespossible to prevent, for example, the portion where the optical fiber112 is fixed (connected) from being damaged by the light irradiated fromoutside. In a case where the optical filter 110 is located on theoptical fiber 112 side of the two condenser lenses, it is possible toreduce the recollection of the light reflected by the optical filter110, but the reflected light may irradiate the portion where the opticalfiber 112 is fixed, which is not preferable. Similarly, in a case wherethe optical filter 110 is located on the opposite side of the opticalfiber 112 relative to the two condenser lenses, there is a risk that thereflected light is recollected to a single point, causing burning out ofa part such as the portion where the optical fiber 112 is fixed.

An effect of the optical filter 110 is described with reference to FIGS.5A and 5B. FIG. 5A is an enlarged drawing of an area of the opticalfilter 110 of FIG. 1. It is assumed that the light, which is propagatedthrough the optical fiber 112 and irradiated from outside, is incidentin the direction of the arrow of FIG. 5A. The reflected light fromoutside, which is reflected by the optical filter 110, irradiates a partof the first light-blocking portion 113 as illustrated by the ellipse ofFIG. 5B. That is, the light reflected by the optical filter 110 is notrecollected, does not irradiate the portion where the optical fiber 112is fixed, and the diameter of the reflected light beam becomes greater,so that the light intensity per unit area becomes weaker accordingly,thereby preventing burning out of the irradiated part of the reflectedlight. Therefore, in a case where the optical filter 110 which is tiledis located between the two condenser lenses, a greater effect can beachieved.

The optical fiber 112 may be a multi-mode optical fiber of which corediameter is, for example, 105 μm and of which cladding diameter is, forexample, 125 μm, or alternatively may be a single-mode optical fiber.For example, NA of the optical fiber 112 may be 0.15 to 0.22.

The first light-blocking portion 113 is a rectangular plate componentprovided with a notched portion through which the protrusion portion 112b of the optical fiber 112 is inserted. An end of the optical fiber 112is projecting from the first light-blocking portion 113. FIG. 4 is anenlarged schematic partially cutout view of the first light-blockingportion of the semiconductor laser module shown in FIG. 1. As shown inFIG. 4, the first light-blocking portion 113 is disposed at an outerperiphery of the protrusion portion 112 b of the optical fiber 112 andseparated from the optical fiber 112.

By separating the first light-blocking portion 113 from the opticalfiber 112, it is possible to restrain heat from being transferred fromthe first light-blocking portion 113 to the optical fiber 112, and thus,an increase in temperature of the first-fixing agent 119, which will bedescribed later, can be restrained.

By providing the first light-blocking portion 113 so that the end of theoptical fiber 112 projects from the first light-blocking portion 113 toan input side of the laser light, it is possible to restrain anon-coupled light from leaking from between the first light-blockingportion 113 and the optical fiber 112, and thus, it is possible to blockthe non-coupled light not being coupled to the optical fiber 112 morereliably.

The optical fiber 112 is inserted through the boot 114 preventing theoptical fiber 112 being bent from damage. Although the boot 114 may be aboot made of metal, the material therefor may not be limitedspecifically, and the boot 114 may be made of rubber, various resin,plastics or the like.

The optical fiber 112 is inserted through the loose tube 115 preventingthe optical fiber 112 being bent from damage. Moreover, the loose tube115 being fastened to the optical fiber 112 may be configured, as aresult, to prevent the optical fiber 112 from being shifted in positionwhen a tensile force is applied to the optical fiber 112 in thelongitudinal direction.

The glass capillary 116 is a round-tube-shaped glass capillary providedwith a through hole. The optical fiber 112 is inserted through thethrough hole of the glass capillary 116. An inner wall of the throughhole of the glass capillary 116 and the cladding portion 112 d of theoptical fiber 112 are fastened with the first-fixing agent 119. Theglass capillary 116 has optical transmittance at wavelengths of laserlights outputted by the semiconductor laser elements 104-1 to 6, and itis preferable that the glass capillary 116 be made of, for example,material of which transmissivity is equal to or greater than 90% atthese wavelengths. It is preferable that the refractive index of theglass capillary 116 be equal to or higher than the refractive index ofthe cladding portion 112 d of the optical fiber 112. The relativerefractive-index difference of the glass capillary 116 relative to thecladding portion 112 d of the optical fiber 112 is, for example, equalto or higher than 0.1% and equal to or lower than 10%. The glasscapillary 116 may be provided with a tapered portion, at alight-emitting side, for facilitating insertion of the optical fiber112.

The light-absorbing element 117 is disposed at an outer periphery of theglass capillary 116 and is fastened to the glass capillary 116 with thesecond-fixing agent 120. The light-absorbing element 117 has opticalabsorptivity at wavelengths of the laser lights outputted by thesemiconductor laser elements 104-1 to 6, and for example, itsabsorptivity is equal to or higher than 30%, or is more preferable to beequal to or greater than 70% at these wavelengths. As a result, thelight-absorbing element 117 absorbs the laser light transmitted throughthe glass capillary 116. Since the light-absorbing element 117 radiatesheat generated by optical absorption, it is preferable that thelight-absorbing element 117 be made of a material, excellent in thermalconductivity, such as a metal component containing Cu, Ni, stainlesssteel, or Fe, a metal containing Ni, Cr, and Ti, or a member providedwith a top-surface-plating layer containing C, ceramics componentcontaining AlN or Al₂O₃, or a member provided with a ceramic layercovering a top surface containing AlN or Al₂O. It is preferable that thelight-absorbing element 117 be connected to the package 101 via a goodheat conductor, not shown in the drawings, since the light-absorbingelement 117 radiates heat generated by optical absorption. It ispreferable that the good heat conductor be made of material, forexample, solder or thermally-conductive adhesive, of which thermalconductivity is equal to or greater than 0.5 W/mk.

The second light-blocking portion 118 is connected to thelight-absorbing element 117, and moreover, the optical fiber 112inserted through the second light-blocking portion 118. As a result, thesecond light-blocking portion 118 prevents the light, transmittedthrough the glass capillary 116 and emitted from an end surface, at anemitting side, of the glass capillary 116, from being emitted to outsidethe semiconductor laser module 100. Therefore, it is preferable that thesecond light-blocking portion 118 be not damaged by the emitted lightand be provided with, for example, such as a metal component containingCu, Ni, stainless steel, or Fe, a member provided with atop-surface-plating layer containing Ni, Cr, Ti or the like, or a memberprovided with dielectric multi-layers. Moreover, it is preferable that asurface, at a side of the glass capillary 116, of the secondlight-blocking portion 118 be inclined or have a curvature so that alight incident thereto is reflected in a direction leaving away from theoptical fiber 112.

The first-fixing agent 119, the second-fixing agent 120, otherultraviolet curable resin, and silicone or the like may be filled into aspace surrounded by the second light-blocking portion 118, thelight-absorbing element 117, and the glass capillary 116.

The first-fixing agent 119 and the second-fixing agent 120 may be madeof a same material or may be made of different materials, and are madeof, for example, epoxy resin, and ultraviolet curable resin such asurethane-based resin or the like. It is preferable that the refractiveindex of the first-fixing agent 119 be equal to or higher than therefractive index of the cladding portion 112 d of the optical fiber 112at 25° C., and it is more preferable that the refractive index of thefirst-fixing agent 119 be equal to or higher than the refractive indexof the cladding portion 112 d of the optical fiber 112 at a temperaturerange at which the semiconductor laser module 100 is being used (forexample, 15° C. to 100° C.). It is preferable that the refractive indexof the second-fixing agent 120 be equal to or higher than the refractiveindex of the glass capillary 116 at 25° C., and it is more preferablethat the refractive index of the second-fixing agent 120 be equal to orhigher than the refractive index of the glass capillary 116 at atemperature range at which the semiconductor laser module 100 is beingused (for example, 15° C. to 100° C.). It may be configured that therefractive indices of the first-fixing agent 119 and the second-fixingagent 120 are approximately equal to the refractive index of the glasscapillary 116 and higher than the refractive index of the claddingportion 112 d of the optical fiber 112. In terms of the refractiveindices of the first-fixing agent 119 and the second-fixing agent 120,relative refractive-index differences thereof relative to, for example,that of the glass capillary 116 are equal to or higher than 0% and equalto or lower than 10%. It is preferable that thicknesses of thefirst-fixing agent 119 and the second-fixing agent 120 in a plane thatis orthogonal to the longitudinal direction of the optical fiber 112 beequal to or greater than 1 μm and equal to or less than 800 μm. It hasbeen known that the refractive index of the ultraviolet curable resincan be lowered by making the ultraviolet curable resin contain fluorineand can be increased by making the ultraviolet curable resin containsulfur, and thus, the refractive index thereof can be adjusted byadjusting amounts of refractive-index-increasing material andrefractive-index-decreasing material.

Hereafter, an operation of the semiconductor laser module 100 accordingto the present embodiment will be explained. When electrical power issupplied from the lead pin 105, each of the semiconductor laser elements104-1 to 6 disposed on the steps outputs a laser light. Each of theoutputted laser light is made become an approximate collimated light byeach of the first lenses 106-1 to 6 and each of the second lenses 107-1to 6 respectively. Then, each of the laser lights are reflected in thedirection of the optical fiber 112 by each of the mirrors 108-1 to 6disposed at a corresponding height. Then, each laser light is condensedby the third lens 109 and the fourth lens 111 to be coupled to theoptical fiber 112. The laser light coupled to the optical fiber 112 isguided by the optical fiber 112 to be outputted to outside thesemiconductor laser module 100. The semiconductor laser module 100prevents unnecessary loss from being produced in the laser light by thesteps of the semiconductor laser elements 104-1 to 6 and the mirrors108-1 to 6. In the present embodiment, if optical powers of the lightsoutputted from the semiconductor laser elements 104-1 to 6 are 11 Wrespectively and coupling efficiencies are 85% respectively, an opticalpower of the light outputted from the semiconductor laser module 100 is56 W.

Herein the way how the laser light condensed by the third lens 109 andthe fourth lens 111 propagates will be explained in detail withreference to FIG. 3. For the purpose of simple description, in FIG. 3,description of refraction of the laser light L3 which will technicallyoccur at an interface corresponding to a refractive index difference ofrespective members is omitted. The laser light L condensed by the thirdlens 109 and the fourth lens 111 becomes a non-coupled light L1 notbeing coupled to the optical fiber 112 and a light L2 being coupled tothe optical fiber 112 and propagating in the optical fiber 112. Althoughalmost of the light L2 coupled to the optical fiber 112 propagates inthe core portion 112 c of the optical fiber 112, guided and outputted tooutside the semiconductor laser module 100, a part of the light L2 iscoupled to the cladding portion 112 d and becomes a light L3 propagatingin the cladding portion 112 d. Sometimes, a part of the light L2propagating in the core portion 112 c leaks from the core portion 112 cto become a light L3 propagating in the cladding portion 112 d.

The first light-blocking portion 113 restrains the non-coupled light L1from being incident to the glass capillary 116, and absorbs a part ofthe non-coupled light L1. The heat produced by this optical absorptionis radiated from the first light-blocking portion 113 to the package101. For restraining the non-coupled light from being incident to theglass capillary 116 reliably, the first light-blocking portion 113 isdisposed at the protrusion portion 112 b of the optical fiber 112. Forthis purpose, it is preferable that the first light-blocking portion 113be not damaged even if a part of the laser light is irradiated, and beprovided with, for example, such as a metal component containing Cu, Ni,stainless steel, or Fe, a member provided with a top-surface-platinglayer containing Ni, Cr, Ti or the like, or a member provided withdielectric multi-layers. For being separated from the optical fiber 112reliably and blocking a light not coupled to the optical fiber 112sufficiently, it is preferable that the first light-blocking portion 113be set to have a distance (clearance) from the optical fiber 112 in aplane which is orthogonal to the longitudinal direction of the opticalfiber 112. Since a beam shape of a laser light becomes elliptic usually,it is preferable that the clearance be equal to or greater than 5 μm andequal to or less than 500 μm in the major axis direction of an ellipse.

As described above, herein the light L3 propagating in the claddingportion 112 d is produced in the cladding portion 112 d.

In the protrusion portion 112 b, the light L3 is confined in thecladding portion 112 d of the optical fiber 112 by the refractive indexdifference of the cladding portion 112 d relative to air thereoutsideand propagates in the cladding portion 112 d of the optical fiber 112.

Then, the light L3 reaches an interface between the cladding portion 112d and the first-fixing agent 119. Herein if the refractive index of thefirst-fixing agent 119 is higher than the refractive index of thecladding portion 112 d, the light L3 is likely to be transmitted throughthis interface. Moreover, the light L3 is the most likely to betransmitted through this interface when the refractive indices of thecladding portion 112 d and the first-fixing agent 119 are identical.Although the light L3 transmitted through this interface (that is,leaking from the optical fiber 112) propagates in the first-fixing agent119, the first-fixing agent 119 is restrained from being damaged sinceits thickness of equal to or less than 800 μm is sufficiently thin andits optical absorption is sufficiently low. It is more preferably thatthe thickness of the first-fixing agent 119 be equal to or less than 5μm.

Subsequently, the light L3 reaches an interface between the first-fixingagent 119 and the glass capillary 116. The light L3 is likely to betransmitted through this interface similarly if the refractive index ofthe glass capillary 116 is higher than the refractive index of thefirst-fixing agent 119. Moreover, the light L3 is the most likely to betransmitted through this interface when the refractive indices of thefirst-fixing agent 119 and the glass capillary 116 are identical.Although the light L3 transmitted through this interface propagates inthe glass capillary 116, the light L3 is transmitted through the glasscapillary 116 since the transmissivity, for example, equal to or greaterthan 90%, of the light L3 at the glass capillary 116 is sufficientlyhigh.

Subsequently, the light L3 reaches an interface between the glasscapillary 116 and the second-fixing agent 120. The light L3 is likely tobe transmitted through this interface similarly if the refractive indexof the second-fixing agent 120 is higher than the refractive index ofthe glass capillary 116. Moreover, the light L3 is the most likely to betransmitted through this interface when the refractive indices of theglass capillary 116 and the second-fixing agent 120 are identical.Although the light L3 transmitted through this interface propagates inthe second-fixing agent 120, the second-fixing agent 120 is restrainedfrom being damaged since its thickness of equal to or less than 800 μmis sufficiently thin and its optical absorption is sufficiently low. Itis more preferable that the thickness of the second-fixing agent 120 beequal to or less than 5 μm.

Subsequently, the light L3 reaches the light-absorbing element 117.Then, the light L3 is absorbed by the light-absorbing element 117 havingoptical absorptivity, for example, equal to higher than 30%, or morepreferably equal to or greater than 70% of absorptivity. Heat generatedby this optical absorption is radiated from the light-absorbing element117 to the package 101.

Herein FIG. 6 is a schematic view showing a relationship between anangle of a light leaking from an optical fiber relative to the center ofthe optical fiber and an optical power thereof. The horizontal axis ofFIG. 6 indicates an angle of a light, propagating in the claddingportion 112 d and then leaking from the optical fiber, relative to thecenter of the optical fiber and is an angle θ in FIG. 3. As shown inFIG. 6, the light leaking from the cladding portion 112 d of the opticalfiber 112 is emitted from the center of the optical fiber 112 to outsidethe angle θa. In this state, it is preferable that the glass capillary116 be of a sufficient length so that a light outputted from the opticalfiber 112 at an angle θa reaches the light-absorbing element 117.Moreover, it is more preferable that the glass capillary 116 be of asufficient length so that a light reflected at, but not absorbed by, thelight-absorbing element 117 reaches the light-absorbing element 117again. For length as such, the glass capillary 116 is of a length ofequal to or greater than 3 mm in the longitudinal direction of the roundtube.

It is preferable that an inner diameter of the round tube of the glasscapillary 116 be equal to or smaller than 0.13 mm for decreasing theamount of the first-fixing agent 119 sufficiently. It is preferable thatthe glass capillary 116 be of, or greater than, a certain thickness sothat heat caused by optical absorption by the light-absorbing element117 does not damage the first-fixing agent 119 and the coated portion112 a of the optical fiber 112, and it is preferable that an outerdiameter of the round tube be, for example, equal to or greater than 1.8mm.

As described above, the semiconductor laser module 100 according to thepresent embodiment obtains an effect below. That is, a non-coupled lightis restrained from being incident to the glass capillary 116 by thefirst light-blocking portion 113. As a result, the first-fixing agent119, the second-fixing agent 120, and the coated portion 112 a or thelike of the semiconductor laser module 100 are restrained from beingdamaged by the non-coupled light.

A refractive index of each member of the semiconductor laser module 100is selected appropriately so that a light propagating in the claddingportion 112 d is likely to leak from the optical fiber at each ofinterfaces of the cladding portion 112 d to second-fixing agent 120.Therefore, since the light leaking as such is restrained from beingreflected at each interface, the light leaking as such is absorbed bythe light-absorbing element 117 effectively.

Moreover, since the semiconductor laser module 100 has the glasscapillary 116 between the optical fiber 112 and the light-absorbingelement 117, the density of the leakage light can be reduced before theleakage light from the optical fiber 112 reaches the light-absorbingelement 117. Hereby an increase in temperature of the light-absorbingelement 117 can be restrained.

Moreover, since the semiconductor laser module 100 includes thelight-absorbing element 117 having a optical absorptivity, the reflectedlight at the light-absorbing element 117 is restrained from damaging thefirst-fixing agent 119, the second-fixing agent 120, and the coatedportion 112 a.

Since the first-fixing agent 119 and the second-fixing agent 120 aresufficiently thin, the semiconductor laser module 100 is restrained frombeing damaged by optical absorption of the first-fixing agent 119 andthe second-fixing agent 120. The semiconductor laser module 100according to the present embodiment obtains the effects described aboveand is a highly reliable semiconductor laser module.

Moreover, since the second light-blocking portion 118 has inclination orcurvature so that a light being incident thereto is reflected in adirection leaving away from the optical fiber 112, and since the lightbeing incident to the second light-blocking portion 118 is reflected andprevented from damaging the first-fixing agent 119 of a tapered portionof the glass capillary 116, the semiconductor laser module 100 is ahighly reliable semiconductor laser module. Since it is not preferablefrom a safety point of view if a light being transmitted through theglass capillary 116 leaks outside the semiconductor laser module 100,the second light-blocking portion 118 prevents the light beingtransmitted through the glass capillary 116 from being emitted tooutside the semiconductor laser module 100. For this reason, thesemiconductor laser module 100 is a highly safe semiconductor lasermodule.

As described above, the semiconductor laser module 100 according to thepresent embodiment is a highly reliable and safe semiconductor lasermodule.

Modified Example

Hereafter, a modified example of the semiconductor laser module in theabove-described embodiment will be explained. The semiconductor lasermodule according to the modified example can be configured by replacingeach of the elements of the semiconductor laser module of theabove-described embodiment with elements of a modified example below.

The first light-blocking portion is not limited to a shape shown in FIG.4. FIG. 7 is an enlarged schematic partially cutout view of a firstlight-blocking portion of a semiconductor laser module according to amodified example. As shown in FIG. 7, a first light-blocking portion 213may be a first light-blocking portion 213 which is a round disk providedwith a hole through which, for example, an optical fiber 212 isinserted. The first light-blocking portion 213 is mounted on a pedestal213 a fixed on a package 201. As described above, the firstlight-blocking portion 213 is not limited to a specific shape as long asthe first light-blocking portion 213 is capable of restraining anon-coupled light from being incident to a glass capillary.

The glass capillary as an optical component may have a refractive indexprofile in a cross section which orthogonal to the longitudinaldirection of the optical fiber. FIG. 8 is a schematic view showingrefractive index of a cross section orthogonal to the longitudinaldirection of the optical fiber of the glass capillary of thesemiconductor laser module according to the modified example. As shownin FIG. 8, the glass capillary of the modified example is made higher inits refractive index, if being more distant from its center, in thecross section orthogonal to the longitudinal direction of the opticalfiber. As a result, this glass capillary is capable of causing theincident light to escape thereoutside effectively. Therefore, the glasscapillary of the modified example is capable of further increasingreliability of the semiconductor laser module.

Moreover, it is preferable that the glass capillary as an opticalcomponent restrain a light emitted from the optical fiber to the glasscapillary from returning to the optical fiber. FIGS. 8 to 11 areschematic cross-sectional views of the cross section orthogonal to thelongitudinal direction of the optical fiber of the glass capillary ofthe semiconductor laser module according to the modified example.

As shown in FIG. 9, although a glass capillary 316 of the modifiedexample is round-shaped in the cross section orthogonal to thelongitudinal direction of the optical fiber, the center of a throughhole 316 a is eccentric from the center C of the glass capillary 316.That is, an optical fiber is inserted through the glass capillary 316 ata position that is eccentric from the center C. As a result, the glasscapillary 316 restrains a light emitted from the optical fiber to theglass capillary 316 from being reflected by the light-absorbing elementand returning to the optical fiber.

As shown in FIG. 10, a glass capillary 416 of a next modified examplemay be rectangular in the cross section orthogonal to the longitudinaldirection of the optical fiber. As a result, the glass capillary 416restrains a light emitted from the optical fiber to the glass capillary416 from being reflected by the light-absorbing element and returning tothe optical fiber. Similarly, the glass capillary may be of a polygonalshape, a flower shape, or a star shape or the like in the cross sectionorthogonal to the longitudinal direction of the optical fiber.

As shown in FIG. 11, a glass capillary 516 may be a two-core capillaryprovided with two through holes as a through hole 516 a and a throughhole 516 b extending in the longitudinal direction of the optical fiber.An optical fiber is inserted through one of the through hole 516 a andthe through hole 516 b of the glass capillary 516. Both the through hole516 a and the through hole 516 b are disposed to be eccentric from thecenter of the glass capillary 516. As a result, in the glass capillary516, a light emitted from the optical fiber to the glass capillary 516is restrained from being reflected by the light-absorbing element andreturning to the optical fiber.

In the glass capillaries of the modified examples described above, sincethe light emitted from the optical fiber to the glass capillary isrestrained from returning to the optical fiber, the first-fixing agent,the second-fixing agent, and the coated portion of the optical fiber arerestrained from being damaged by the light reflected by thelight-absorbing element. Therefore, the glass capillaries of themodified examples are capable of increasing reliability of thesemiconductor laser module.

As shown in FIG. 12, a glass capillary 616 of another modified examplemay be provided with a light-scattering means as, for example, a bubble616 b. As a result, the glass capillary 616 is capable of making thelight being incident from the cladding portion be scattered by thebubble 616 b to be absorbed by the light-absorbing element effectively.This glass capillary restrains the first-fixing agent, the second-fixingagent, and the coated portion or the like of the optical fiber frombeing damaged by making the light-absorbing element absorb the lightemitted from the optical fiber to the glass capillary effectively.Therefore, the glass capillaries of the modified examples are capable ofincreasing the reliability of the semiconductor laser module.

The light-absorbing element may have a profile for an opticalabsorptivity at a wavelength of the laser light along the longitudinaldirection of the optical fiber. FIG. 13 is a schematic view showing arelationship between distance from an end surface, at an incident side,of the glass capillary in the longitudinal direction of the opticalfiber and optical absorptivity of the light-absorbing element of thesemiconductor laser module according to the modified example. As shownin FIG. 13, optical absorptivity of a light-absorbing element 717according to the modified example is made higher at a side emitting alaser light than at a side into which the laser light is incident. Inthis state, as shown in FIG. 13, optical absorptivity of thelight-absorbing element 717 is higher at a position where a laser lightL, as a light leaking from, for example, the cladding, is reflected onceby the light-absorbing element 717 and is irradiated to thelight-absorbing element 717 for the second time than at a position wherethe laser light L is irradiated to the light-absorbing element at first.This results in restraining the second-fixing agent from being damagedby heat produced by optical absorption concentrated at a side into whichthe laser light L is incident. Therefore, the light-absorbing element717 of the modified example is capable of increasing the reliability ofthe semiconductor laser module.

As a specific example of the light-absorbing element having a profile ofoptical absorptivity, average surface roughness of a plane, of thelight-absorbing element of the modified example, fastened to the glasscapillary is made smaller at a side of the fourth lens(light-incident-side) along the longitudinal direction of the opticalfiber. Herein the absorptivity of metal becomes higher if the surfaceroughness of the plane into which a light is incident is greater.Therefore, the optical absorptivity of this light-absorbing element issmaller at the side of the fourth lens. That is, in this light-absorbingelement, the second-fixing agent is restrained from being damaged byheat produced by optical absorption concentrated at a side into whichthe laser light L is incident. Therefore, the light-absorbing element ofthe modified example is capable of increasing the reliability of thesemiconductor laser module.

FIG. 14 is an enlarged schematic cross-sectional view of an opticalfiber, a glass capillary, and a light-absorbing element of thesemiconductor laser module according to the modified example. As thefirst light-blocking portion and the second light-blocking portion, afirst light-blocking portion 113A and a second light-blocking portion118A shown in FIG. 14 may be provided instead of the firstlight-blocking portion 113 and the second light-blocking portion 118shown in FIGS. 2 and 3. These first light-blocking portion 113A and thesecond light-blocking portion 118A are dielectric multi-layers formed atan end surface of the glass capillary 116. It is preferable thatreflectivity of this dielectric multi-layer be equal to or greater than90% at wavelengths of laser lights outputted by the semiconductor laserelements 104-1 to 6. It is preferable that a distance (clearance)between the first light-blocking portion 113A and the optical fiber 112be equal to or greater than 5 μm and equal to or less than 500 μm in amajor axis direction of a beam, shaped in ellipse, of the laser light.Although the second light-blocking portion 118A shown in FIG. 14 isformed from an end surface of the glass capillary 116 to a taperedportion of the through hole, the second light-blocking portion 118A maynot be formed at the tapered portion alternatively.

By providing the second light-blocking portion 118A, it is possible torestrain the light, transmitted through the glass capillary 116 andemitted from the end surface, at an emitting side, of the glasscapillary 116 from being emitted to outside the semiconductor lasermodule 100 and make the light-absorbing element 117 absorb the light.

The semiconductor laser module may be provided with various kinds ofradiation structure. As a result, semiconductor laser module is capableof restraining the second-fixing agent from being damaged by temperatureincreased by optical absorption of the light-absorbing element. For suchradiation structures, a radiation structure being provided with a finair-cooling an light-absorbing element or a package and a radiationstructure or the like being provided with a circulation pump and coolinga light-absorbing element or a package with water or various kinds ofrefrigerant can be chosen.

As described above, the semiconductor laser module of the presentembodiments or the modified examples is a highly reliable semiconductorlaser module.

The present invention is not limited to the above-described embodiments.The present invention includes a configuration appropriately combiningthe above-described elements. Further effects or modification examplescan be derived by an ordinary skilled person in the art easily.Therefore, further wide aspects of the present invention are not theabove-described embodiments, and various modifications may be made.

As described above, the semiconductor laser module according to thepresent invention is suitable mainly for use in high-outputsemiconductor laser module.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A semiconductor laser module comprising: apackage; a plurality of semiconductor laser elements provided in thepackage; a member having a plurality of mounting surfaces on which thesemiconductor laser elements are mounted, the mounting surfaces beingseparated from a bottom surface of the package by respective distances,the distances being gradually different from each other in a manner thatthe mounting surfaces form a step-like form; a plurality of lensesconfigured to collimate respective laser beams emitted from thesemiconductor laser elements; a plurality of reflection mirrorsconfigured to reflect the respective laser beams; a condenser lens unitconfigured to condense the laser beams; an optical fiber where theoptical beams condensed by the condenser lens unit are opticallycoupled; and an optical filter disposed on optical lines of therespective laser beams reflected by the reflection mirrors andconfigured to reflect light having wavelengths different from thewavelengths of the laser beams.
 2. The semiconductor laser moduleaccording to claim 1, wherein the condenser lens unit include two ormore independent condenser lenses which condense the laser beams in avertical direction and in a horizontal direction, respectively.
 3. Thesemiconductor laser module according to claim 2, wherein the opticalfilter is disposed between two of the independent condenser lensesincluded in the condenser lens unit.
 4. The semiconductor laser moduleaccording to claim 1, wherein the optical filter is tilted relative tooptical axes of the laser beams reflected by the reflection mirrors. 5.The semiconductor laser module according to claim 1, wherein the opticalfilter is configured to reflect light having a wavelength greater thanwavelength of the laser beams.